The present invention relates to a fiber laser configured to suppress internal damage caused by reflected light, while also avoiding a decline in the intensity of output light.
A fiber laser that amplifies and emits signal light through a rare-earth doped fiber is utilized as one of the laser devices employed in processing machines and medical equipment that use laser beams, such as a surgical knife. A fiber laser of this type may emit large pulsed output light, in which a duty ratio, i.e. , a ratio between an OFF time and an ON time is, for example, 10:1. Such a fiber laser with a large duty ratio may emit amplified spontaneous emission (ASE) light in a state where the pulsed output light is not emitted. A part of the emitted ASE light may be reflected at a body to be processed, that is supposed to be irradiated with the signal light, and may be incident from an emitting end of the fiber laser. When the reflected ASE light is incident on the fiber laser in such a manner, the reflected light is amplified in the rare-earth doped fiber, causing the internal part of the fiber laser (a light source and the like) to potentially be damaged by the reflected light that has been amplified.
Therefore, removal of unnecessary ASE light has been performed. Japanese Patent Application Laid-Open (JP-A) No. 2001-83557 discloses a laser device that removes ASE light with a filter. Further, JP-A No. 03-235924 details a light amplifier that removes ASE light with a filter.
The laser device of JP-A No. 2001-83557, and the optical fiber amplifier of JP-A No. 03-235924 are configured in such a manner that the signal light emitted from a light source is amplified in a rare-earth doped fiber that is then transmitted through a filter. A wavelength band of the light that is to be transmitted through the filter is narrowed in accordance with the wavelength band of the signal light so that only the light with the same wavelength as the signal light can be transmitted. The wavelength band of the light to be transmitted through the filter and the wavelength band of the signal light are in accordance with each other, such that only the signal light can be transmitted through the filter, with the ASE light that is not transmitted through the filter being removed.